Mesoporous Amorphous Bulk Material Electrodes for Ultrahigh Volumetric Capacity Electrochemical Capacitors

Abstract Retaining satisfactory electrochemical performances under high‐mass electrode‐active‐matter loadings is important for energy storage. However, the performance decreases with increasing mass loadings due to a reduction in the ion/electron transport. In this study, a novel mesoporous amorphous bulk (MAB) material strategy is proposed. Co‐based hydroxide KCo_1.3(OH)_3.6 is directly electro‐deposited on the Ni foam for cathode. Comprehensive structural characterizations confirm the mesoporous, amorphous, and bulk features for KCo_1.3(OH)_3.6. The fabricated whole MAB‐KCo_1.3(OH)_3.6@Ni electrode exhibits an ultrahigh full volumetric capacity (123.7 mAh cm⁻³) with high KCo_1.3(OH)_3.6 mass loading (11.7 mg cm⁻²) and excellent cycling stability. Along with the MAB‐KCo_1.3(OH)_3.6, the mesoporous amorphous features enable fast ion diffusion and provide sufficient electroactive sites for redox reactions. In addition, the bulk nature not only facilitates the electron mobility but also guarantees structural and chemical stability. Therefore, the proposed MAB strategy and explored KCo_1.3(OH)_3.6 material demonstrate considerable prospects for designing electrode materials and practical applications.